Laser micromachining of CNT/Fe/Al_2O_3 nanocomposites

CNT/Fe/Al2O3 mixed powders were synthesized from Fe/Al2O3 nanopowders using thermal CVD for the homogeneous dispersion of carbon nanotubes CNTs. CNTs consisted of MWNT, and the diameter was approximately 20-30 nm. After sintering, CNTs were homogenously located throughout Al2O3 grain boundary and were buckled. A femto-second laser installed with special optical systems was used for micromachining of the nanocomposites. The relationship between material ablation rate and energy fluence was theoretically investigated and compared with experimental results from cross-sectional SEM analysis. The nanocomposites which have higher content of CNT show a fairly good machining result due to its higher thermal conductivity and smaller grain size as well as lower light transmittance.

Finite element simulation of the micromachining of nanosized-silicon-carbide-particle reinforced composite materials based on the cohesive zone model

A finite element method based on the cohesive zone model was used to study the micromachining process of nanosized silicon-carbide-particle(SiCp) reinforced aluminum matrix composites. As a hierarchical multiscale simulation method, the parameters for the cohesive zone model were obtained from the stress-displacement curves of the molecular dynamics simulation. The model considers the random properties of the siliconcarbide-particle distribution and the interface of bonding between the silicon carbide particles and the matrix.The machining mechanics was analyzed according to the chip morphology, stress distribution, cutting temperature, and cutting force. The simulation results revealed that the random distribution of nanosized SiCp causes non-uniform interaction between the tool and the reinforcement particles. This deformation mechanics leads to inhomogeneous stress distribution and irregular cutting force variation.

Fabrication of Ordered Micro/Nanostructures Using Probe‑Based Force‑Controlled Micromachining System

This paper presents a probe-based force-controlled nanoindentation method to fabricate ordered micro/nanostructures.Both the experimental and finite element simulation approaches are employed to investigate the influence of the interval between the adjacent indentations and the rotation angle of the probe on the formed micro/nanostructures.The non-contacting part between indenter and the sample material and the height of the material pile-up are two competing factors to determine the depth relationship between the adjacent indentations.For the one array indentations,nanostructures with good depth consistency and periodicity can be formed after the depth of the indentation becoming stable,and the variation of the rotation angle results in the large difference between the morphology of the formed nanostructures at the bottom of the one array indentation.In addition,for the indentation arrays,the nanostructures with good consistency and periodicity of the shape and depth can be generated with the spacing greater than 1μm.Finally,Raman tests are also carried out based on the obtained ordered micro/nanostructures with Rhodamine probe molecule.The indentation arrays with a smaller spacing lead to better the enhancement effect of the substrate,which has the potential applications in the fields of biological or chemical molecular detection.

Review of micromachining of ceramics by etching

In the last two decades, there has been an enormous surge in interest in ceramic materials and, as a result, there have been significant advances in their development and applications. Their inherent properties, such as capability of operating at temperatures far above metals, high level of hardness and toughness, low coefficient of thermal expansion and high thermal conductivity rendered ceramics to be one of the leading engineering materials. Many research works have been conducted in the past few years on machining of advanced ceramics using different processing methods in order to obtain a better surface roughness, higher material removal rate and improved tool life. Micromachining using chemical etching is one of those methods that do not involve the problem of tool life and direct tool-work piece contact. However, only a few research works have been done on micromachining of ceramics using chemical etching. Hence, study of chemical machining of advanced ceramics is still needed as the process has found wide application in the industry because of its relative low operating costs. In this work, we summarize the recent progresses in machining of different types of advanced ceramics, material processing methods such as wet etching and dry etching, and finally the prospects for control of material removal rate and surface quality in the process of ceramic micromachining.

Micro thermal shear stress sensor based on vacuum anodic bonding and bulk-micromachining

This paper describes a micro thermal shear stress sensor with a cavity underneath, based on vacuum anodic bonding and bulk micromachined technology. A Ti/Pt alloy strip, 2μm×100μm, is deposited on the top of a thin silicon nitride diaphragm and functioned as the thermal sensor element. By using vacuum anodic bonding and bulk-si anisotropic wet etching process instead of the sacrificial-layer technique, a cavity, functioned as the adiabatic vacuum chamber, 200μm×200μm×400μm, is placed between the silicon nitride diaphragm and glass （Corning 7740）. This method totally avoid adhesion problem which is a major issue of the sacrificial-layer technique.

Poly-Silicon Micromachined Switch

By using LPCVD SiO 2 and poly silicon as sacrificial layer and cantilever respectively,a poly silicon micromachined RF MEMS(radio frequency microelectronic mechanical system) switch is fabricated.During the fabrication process,the stress of poly silicon is released to prevent poly silicon membrane from bending,and the issue of compatibility between RF switch and IC process technology is also resolved.The low residual tensile stress poly silicon cantilever is obtained by the optimization.The switch is tested,and the preliminary test results show:the pull down voltage is 89V,and the switch speed is about 5μs.The switch provides the potential to build a new fully monolithic integrated RF MEMS for radar and communications applications.

Pressure effects in AlAs/Inx Ga1-xAs/GaAs resonant tunnelling diodes for application in micromachined sensors

This paper reports the current-voltage characteristics of [001]-oriented AlAs/InxGa1-xAs/GaAs resonant tunnelling diodes （RTDs） as a function of uniaxial external stress applied parallel to the [110] and the [1^-10] orientations, and the output characteristics of the GaAs pressure sensor based on the pressure effect on the RTDs. Under [110] stress, the resonance peak voltages of the RTDs shift to more positive voltages. For [1^-10] stress, the peaks shift toward more negative voltages. The resonance peak voltage is linearly dependent on the [110] and [1^-0] stresses and the linear sensitivities are up to 0.69 mV/MPa, -0.69 mV/MPa respectively. For the pressure sensor, the linear sensitivity is up to 0.37 mV/kPa.

Nonlinearity analysis of piezoelectric micromachined ultrasonic transducers based on couple stress theory

This paper studies the static deformation behavior of a piezoelectric micromachined ultrasonic transducer （PMUT） actuated by a strong external electric field. The transducer membrane consists of a piezoelectric layer, a passive layer and two electrode layers. The nonlinearities of the piezoelectric layer caused by electrostriction under a strong electric field are analyzed. Because the thickness of the transducer membrane is on the microscale, the size dependence of the deformation behavior is evaluated using the couple stress theory. The results show that the optimal ratio of the top electrode diameter and the membrane diameter is around 0.674. It is also found that this optimal value does not depend on any other parameters if the thicknesses of the two electrodes are negligible compared with those of the piezo- electric and passive layers. In addition, the nonlinearities of the piezoelectric layer will become stronger along with the increase of the electric field, which means that softening of the membrane stiffness occurs when a strong external electric field is applied. Meanwhile, the optimal thickness ratio for the passive layer and the piezoelectric layer is not equal to 1.0 which is usually adopted by previous researchers. Because there exists size dependence of membrane deforma-tion, the optimal value of this thickness ratio needs to be greater than 1.0 on the microscale.

Design of a hexagonal air-coupled capacitive micromachined ultrasonic transducer for air parametric array

An air parametric array can generate a highly directional beam of audible sound in air,which has a wide range of applications in targeted audio delivery.Capacitive micromachined ultrasonic transducer(CMUTs)have great potential for air-coupled applications,mainly because of their low acoustic impedance.In this study,an air-coupled CMUT array is designed as an air parametric array.A hexagonal array is proposed to improve the directivity of the sound generated.A finite element model of the CMUT is established in COMSOL software to facilitate the choice of appropriate structural parameters of the CMUT cell.The CMUT array is then fabricated by a wafer bonding process with high consistency.The performances of the CMUT are tested to verify the accuracy of the finite element analysis.By optimizing the component parameters of the bias-T circuit used for driving the CMUT,DC and AC voltages can be effectively applied to the top and bottom electrodes of the CMUT to provide efficient ultrasound transmission.Finally,the prepared hexagonal array is successfully used to conduct preliminary experiments on its application as an air parametric array.

DESIGN,FABRICATION,TESTING AND MECHANICAL ANALYSIS OF BULK-MICROMACHINED FLOWMETERS

Micromachined piezoresistive flowmeters with four different types of sensing struc- tures have been designed,fabricated and tested.Piezoresistors were defined at the end of the sensors through p-diffusion,and their values were about 3.5kΩ.Wheatstone bridge was configured with the piezoresistors in order to measure the output response.The output voltage increases with increasing flow rate of air,obeying determined relationships.The testing results show that the sensors that are designed for measuring 10L/M in full operational range have desired sensitivities.The sensor chip is manufactured with bulk-micromachining technologies,requiring a set of seven masks.

A Silicon Micromachined Gyroscope Driven by the Rotating Carrier Self

This paper reported a silicon micromachined gyroscope which is driven by the rotating carrier's angular velocity,the silicon was manufactured by anisotropy etching.The design,fabrication and packing of the sensing element were introduced in the paper.The imitation experimentation and performance test have certificated that the principle of the gyroscope is correct and the gyroscope can be used to sense yawing or pitching angular velocity of the rotating carrier,and the angular velocity of the rotating carrier itself.

Improved Design and Modeling of Micromachined Tuning Fork Gyroscope Characterized by High Quality Factor

This paper proposes an improved design of micromachined tuning fork gyroscope （M-TFG） to decouple the cross talk between driving and sensing directions better and to increase resolution. By employing dual-folds spring suspension, the drive mode and the sense mode are mechanically decoupled. Through careful layout design of the location of the dual-folds spring suspension and the drive combs, the mechanical coupling effect is further decreased by isolating the unwanted excitation from detection. The quality factor investigation demonstrates that high quality factor can be attained by using this structure, which can bring in accurate resolution. As a result, this design has the potential to accomplish low bias drift and accurate resolution for initial level applications.

Influence of the instability of angular velocity of the rotating carrier itself on the stability of silicon micromachined gyroscope

In order to find out the influence of the instability of angular velocity of the rotating carrier itself on the stability of silicon micromachined gyroscope, the digital models for relative error of the high and low damping gyroscope's output signal are given respectively, based on the motion equations of the silicon micromachined gyroscope. Theory proves that the output signal error of the silicon micromachined sensor is mainly caused by the instability of damping factor and the angular velocity of the rotating carrier itself. The experiment result indicates that the error of proportionality coefficient of output voltage which is caused by the instability of the angular velocity of the rotating carrier itself reaches to 4.1 %. Theoretical demonstration and experimental verification show that the instability of angular velocity of the rotating carrier itself has an important effect on the stability of low damping silicon micromachined gyroscope.

Design and simulation of a tuning fork micromachined gyroscope with slide film damping

A novel tuning fork micromachined gyroscope, based on slide-film damping, is presented. The electrostatic driving gyroscope consists of two driving masses each of which supports one sensitive mass. The angular rate is sensed by the differential capacitances consisted of movable bar electrodes and fixed bar electrodes located on the glass wafer. The gyroscope can operate at atmospheric pressure with slide film damping in the driving and sensing directions, eliminate vacuum packaging and restrain cross-axis acceleration signal. The results of design and simulation show that the driving and sensing mode frequencies are 3 106 Hz and 3 175 Hz,respectively, and the Q-values in driving and sensitive modes are 1 721 and 1 450 respectively. The design resolution is 0.025°/s.

FT-638 G Mini Micromachine for Kidney Imaging

The FT-638 mini micromachine for kidney imaging, manufactured by the Beijing Nuclear Instrument Factory, shows the curve lines of the human kidney and records various data and indexes in clinical examination, not only providing accurate data for diagnosis but also monitoring kidney translating. The FT-638G mini machine for thekidneys is a new product which

激光微加工技术在航空发动机维护和翻修工作中的应用

航空发动机长期处于高温、高频率的工况时,发动机叶片等零部件老化速度较快,需要对发动机定期开展维护和翻修工作。使用激光微加工技术可以进行快速的表面处理,包括进行涂覆层的重构、去除表面污垢等。分析在航空发动机维护和翻修工作中如何使用激光微加工技术进行微纳构造处理、激光清洗,以及如何使用增材制造技术,帮助维修技术人员了解激光微加工技术的特点和应用方法,提高航空发动机维护和翻修工作水平,保证发动机处于正常工作状态。

基于ScAlN薄膜的高频PMUT阵列的设计与制造

高频压电微机械超声换能器(PMUT)应用于各种场景,如指纹识别、无损检测、医疗成像。在当前非侵入式血管成像应用中,存在换能器使用锆钛酸铅压电陶瓷(PZT)及局限于1-D PMUT阵列的问题。设计并制作了一种基于ScAlN材料压电薄膜的2D-PMUT阵列。为了进一步得到阵列最佳的输出性能,降低栅瓣影响,设计了间距为波长的1/2(300μm)的并联六边形阵列,增大了填充因子,降低了阻抗,提高了输出电流。采用SOI晶片作为PMUT的基本结构,设计了微机电系统(MEMS)工艺流程,并完成了晶片制作。通过扫描电子显微镜和聚焦离子束切割确定PMUT的形貌和结构尺寸,并且测得在水中的谐振频率为2.36 MHz。仿真与测试结果表明,测试误差为9.2%,位移灵敏度较好,有望满足非侵入式血管成像应用需求。

短脉冲激光加工微结构及其成型技术研究

短脉冲激光具有高精度、非接触和高可控性等优点,可以针对各种材料进行表面精细加工。如在医用钛合金表面加工出不同形貌、尺寸的微结构,能够有效地改善植入物表面生物活性。利用短脉冲激光在材料加工上的优势,开展了纳秒激光脉冲烧蚀试验,探究纳秒激光与钛合金间的相互作用。阐明钛合金表面火山坑微结构的形成机理,并开展多脉冲激光参数试验,研究激光参数对微结构成型的影响,建立参数与特征尺寸间的映射关系。该研究可以获得具有特定尺寸、高加工质量的微结构,有助于短脉冲激光微加工技术的应用,具有良好的学术和工程意义。

PCD微细刀具的皮秒激光加工特性研究

锋利且耐磨的微细刀具在高精密微细加工中扮演着不可或缺的角色。金刚石材料因卓越的硬度及导热性能、极高的耐磨性而备受推崇,因此被广泛应用于制造锋利耐用的切削刀具。近年来,金刚石微细刀具已成为研究的焦点,但其制备复杂、成本高昂等问题限制了大规模商业化应用。本研究采用皮秒脉冲激光制备聚晶金刚石(PCD)微细刀具,系统研究了激光切割参数,包括脉冲能量、脉冲间距、激光波长以及材料特性(如PCD晶粒尺寸等)对加工结果的影响。揭示了皮秒脉冲激光加工PCD刀具刃口及表面的形成机理。皮秒激光加工后的PCD表面粗糙度达到Ra 200nm,制备出的PCD微细刀具具有良好的无氧铜及硬质合金切削性能。

表面织构电解加工技术研究进展

表面织构在能源、光学、电子、信息技术、生物和摩擦学等领域具有重要应用,其加工工艺是制造技术研究的重要内容。由于所加工表面织构具有无毛刺、翻边等优点,电解加工成为表面织构的重要制造技术方法和技术研究热点,故详细介绍了五种典型表面织构电解加工技术在方法创新、材料去除机制、加工过程建模及加工工艺等方面的研究进展,给出了电解加工表面织构的典型结构和材料,指出提高加工效率和加工自动化程度是未来表面织构电解加工技术的发展趋势。